fix misnomer in msc_a.c: codec_cn -> codec_assigned

Before the codec filter, it would have been the CN side codec, but now
it is only the codec that the RAN reports as assigned, fed into the
codecs filter.

(prep for upcoming change in this code, to support AMR rate selection.)

Change-Id: Ie7966099c5565013018734b0c2028484c24341a7
diff --git a/src/libmsc/msc_a.c b/src/libmsc/msc_a.c
index a933bd2..4fa9676 100644
--- a/src/libmsc/msc_a.c
+++ b/src/libmsc/msc_a.c
@@ -1462,7 +1462,8 @@
 	}
 
 	if (codec_if_known) {
-		const struct codec_mapping *codec_cn;
+		const struct codec_mapping *codec_assigned;
+
 		/* For 2G:
 		 * - The Assignment Complete has returned a specific codec (e.g. FR3 for AMR FR).
 		 * - Set this codec at the MGW endpoint facing the RAN.
@@ -1476,9 +1477,9 @@
 		 * - ran_msg_iu.c always returns FR3 (AMR FR) for the assigned codec. Set that at the MGW towards CN.
 		 * - So the MGW decapsulates IuUP <-> AMR
 		 */
-		codec_cn = codec_mapping_by_gsm0808_speech_codec_type(codec_if_known->type);
+		codec_assigned = codec_mapping_by_gsm0808_speech_codec_type(codec_if_known->type);
 		/* TODO: use codec_mapping_by_gsm0808_speech_codec() to also match on codec_if_known->cfg */
-		if (!codec_cn) {
+		if (!codec_assigned) {
 			LOG_TRANS(cc_trans, LOGL_ERROR, "Unknown codec in Assignment Complete: %s\n",
 				  gsm0808_speech_codec_type_name(codec_if_known->type));
 			call_leg_release(msc_a->cc.call_leg);
@@ -1497,10 +1498,10 @@
 		/* Update RAN-side endpoint CI from Assignment result -- unless it is forced by the ran_infra, in which
 		 * case it remains unchanged as passed to the earlier call of call_leg_ensure_ci(). */
 		if (msc_a->c.ran->force_mgw_codecs_to_ran.count == 0)
-			rtp_stream_set_one_codec(rtps_to_ran, &codec_cn->sdp);
+			rtp_stream_set_one_codec(rtps_to_ran, &codec_assigned->sdp);
 
 		/* Update codec filter with Assignment result, for the CN side */
-		cc_trans->cc.codecs.assignment = codec_cn->sdp;
+		cc_trans->cc.codecs.assignment = codec_assigned->sdp;
 	} else {
 		/* No codec passed in Assignment Complete, set 'codecs.assignment' to none. */
 		cc_trans->cc.codecs.assignment = (struct sdp_audio_codec){};